The invention relates to a method of manufacturing a cathode ray display tube whose inner space has a phosphor coating which can be excited to luminescent emission, said inner space being evacuated by means of a vacuum pump and being subsequently sealed in a gaslight manner.
Display tubes of this type are, for example field emission guns (see Information Display 5, 1989, pp. 17 et seq., or IEEE Trans. E.D. 36, 1989, pp. 225 etc.). Such tubes must also be subsequently evacuated (see Valvo Berichte, 1974, pp. 77, et seq.).
The emission may be stimulated in an arbitrary manner, particularly by means of electron beams. It is known (Philips Technical Review 1989, pp. 335 et seq.) that the luminance of the light decreases with time often referred to as aging or (degradation) at a given electron irradiation intensity, dependent on the quantity of charge of the electron bombardment.
OH groups deposited on phosphor crystals are primarily responsible for the degradation, particularly when silicate-containing binding materials are used in manufacturing the phosphor coating.
Hitherto it has been attempted to decrease the degradation by heating the phosphor coating to approximately 350.degree. C. However, only limited success was obtained with this method.
For example, at relatively low electron energies up to 5 keV, as are usual in flat cathode ray tubes, the heat treatment of the phosphor coating in vacuo at 350.degree. C. does not lead to an adequate decrease of the degradation, because the phosphor surface changes at this high temperature to such an extent that this leads to a greater sensitivity to electron bombardment. However, at lower temperatures of approximately 100.degree. C., the removal of the OH groups from the phosphor surface is much less effective.